I guess csm players like me will rejoice... i can finally have my csm undivided tact squad paired with blood letters if the csm dex does allow us to summon our allies it will definitely bring back the combos to the table once again not seen since CSM 3.5

battle brothers - these allies are truly freinds and benefit from each othersuniversal special rules, psychic powers, and everything, they act as one force.

allies of convenience - these allies will fight together if they have a common foe, they do not get to benefit from each others USR or powers, and in effect act as independant armies on the table.

desperate allies - these allies only fight in dire straights and gain no benefit from each other. you must roll a d6 if the roll is failed your allies do nothing for the tunr as they are whatching you for betrayal.

not before the apocolypse - these armies listed here can never be allies.

allies is very random, tyranids have NO allies at all. everyone else can almost all ally in some form or another.

We don't exactly know the full rules of allies, but I can tell you the allies matrix is accurate and someone posted the rulebook version of it,

Brother in Arms = Can join units + Use friendly psychic powers.Grudging Alliance = Cannot join units + cannot use friendly psychic powers.Unholy Alliance = Same as the above but if allied units are within 6" of your own units, roll a D6, on a 1 the allied unit? won't do anything.

This is probably just a simplified explanation so there maybe more to it.

This one I'm really looking forward to. Everyone's jumpy, the Tau have awesome firepower, and if you put enough shield drones on the Crisis Suits, they get VERY annoying to deal with. By the time you do, the SangGuard are in your face.

2) 12-18 Obliterators + Fateweaver + Chaos Bastion

Ugh! This one gives me heartburn. What's more annoying than playing against Fateweaver? Well, how about 3+ cover with re-rolls for one of the nastiest shooting units in the game? Add in some Bloodcrushers and... ugh!

3) Orks with 90 Lootas In A Bastion or Aegis Defense Line

Gonna happen. Gonna suck too. Especially if they can take a Farseer too. :/

4) Eldar Runes of Warding For Everyone.

This is actually a good thing, since Magic Psykers are going to be so LOL-tastic.

5) Blood Angels + IG

Decent of Angels + Astropath = 2+ reserve rolls for the 2/3rds of your jumpers that you put in a single reserve group. Fun!